Practice or play ball and method of making same



y 1, 1956 R. w. POOLEY ET AL 2,743,931

PRACTICE 0R PLAY BALL AND METHOD OF MAKING SAME Filed Feb. 26, 1953INVENTORS R. M P0015) A. C. KOf/lP/V BY .A T T ORNEY United StatesPatent PRACTICE oR PLAY BALL AND METHOD or MAKING SAME ApplicationFebruary 26, 1953, Serial No. 339,072

6 Claims. emu-199 v This invention relates to la practice or play balland method'of making the same. 'More particularly it relates toapractice or play ball which represents an improvement in the type ofball shown in Barton U. S. Patent 2,484,397. In particular, the ball ofour invention exhibits greatly improved'dime'nsional stability, sharperdefi nition and retention. of a molded surface pattern such as a dimpledesign, and closer simulation of regulation balls, e. g., golf balls orbaseballs, than is possible by prior art practice.

The practice golf ball which is the subject matter of the Barton patentis a spherical mass of closed-cell expanded plasticized polyvinylchloride closely simulating a regulation golf ballin size and appearancebut characterized by its lightweight, its deadness, its short flightwhen struck with a golf club and its ability to substantially duplicatethe flight characteristics ofa regular golf ball except on a muchsmallerscale. The specific exemplifications of practice golf b'a'lls given inthe Barton patent utilize a high-boiling organicliquid plasticizer whichis capable of dissolving powdered polyvinyl chloride upon heating toform a gel"which upon cooling retain the closed-cell structure which isan essential characteristic of the Barton ball.

In the accompanying drawings:

Fig. l.portrays a pre form .ofraw stock used for making the core of theball;

Fig. 2'shows the beginning of the miniature molding operation; v

Fig. 3 shows the end of th'elminiature 'molding operation;

Fig. 4 portrays the end ofthe 'expanding step applied to the miniaturecore;

Fig. 5 shows the expanded .core with the fpaint which is to form theshell applied thereto;

Fig. 6 shows the end of the idirn'pling operation used in making apractice glolfba'll, and

Fig. 7 shows, on a reduced scale, a practice or play baseball made inaccordance with our invention.

The present invention'is based upon our discovery that a practice orplay ball which has exceptionally improved size dimensional stabilityand which is far superior, from the standpoints of appearance andsimulation of a regulation ball such as a regulation golf ball or aregulation baseball, to an expanded closed-cell ball consisting ofpolyvinyl chloride plas'ticized with an organic liquid plasticizer andcontaining no vulcanizablefelastomer is obtained by forming the ballwith aninner core of closedcell expanded polyvinyl chloride orequivalent vinyl resin plasticized with both a high-boiling organicliquid plasticizer and a vulcanizable rubberymateria1 which beforevulcanization is compatible withand capable of plasticizing the vinylresin, this rubbery copo'lymer being vulcanized at an appropriate'tim'eduring the formation of the ball, and a thin continuoussurrounding outershell formed of unexpanded plastic, this shell 'being-sufliciently toughto impart an exceedingly long service life, being sufiiciently flexibleso that the-ball has substantially the playing behavior of the'expalnd'ed"core by itself, that is, the

playing characteristics which it would have if the shell were omitted,and being capable of taking and retaining over the life of the ball anysharply defined outer pattern imparted thereto in a final moldingoperation.

The playing ball of our invention exhibitsseveral important advantagesover prior art balls of this'general type. A major advantage is that therubbery material used in the core not only functions as aplasticizer-for the vinyl resin during the processing and formation ofthe ball but is fixed or mechanically locked by vulcanization so that inthe finished ball it forms a sort of molecular network all through thecore, this network being elastic, i. e., self-retractible upondeformation, and-serving to me.- chanically lock the closed-cellstructure of the core against dimensional change because the vulcanizedrubber component, although flexible, tends always to resume the sizewhich it had at the end of the vulcanization, which in this process itcompleted at the end of the expansion cycle. Thus it will be seen thatthe rubbery component behaves very difierently in a closed-cell resinousstructure from the high-boiling organic liquid plasticizers commonlyused for vinyl resins like polyvinyl chloride. In any event, regardlessof theory, the ball of our invention has far greater resistance tochange in size, shape, or dimension than a ball wherein the plasticizerfor the vinyl resin consists of high-boiling organic liquid material. Asecond major advantage-of the ball 'of our invention is that the toughouter plastic shell contributes far greater durability and resistance tosurface failure upon prolonged use, for example in the case of apracticegolf ball through successive hard hits made by a golf, club, than wouldbe possessed'by the core alone and at the same tiine gives greatlyimproved definition of a pattern impressed injthe surface of thefinished ball so that, in the case of -a practice golf ball, it morestrikingly resembles a'regulation golf ball than a ball in which dimpledefinition is imparted directly to the surface of the closed-cell.plas-. ticized polyvinyl chloride. Likewise, in the case of. :apractice baseball, the shell gives sharp definition of simulatedstitching and retention of this pattern indefinitely. Another advantageis that the use of our shell enables the production of a perfectlywhiteball even though th'e core may be formulated from a coloredcomposition. Thus, it allows the use of a blowing agent which causesdiscoloration of'the core, one such blowing agentfbeingdinitrosopentamethylenetetramine (Unicel NDi") which causes the corematerial of our invention to be light't an in color and, therefore,unattractive on the surface of the finished ball. The shell istenaciously adhered to the core by integral bonding thereto duringthemanufacture of the ball and does not-separatetherefrom during thelife of the ball. The dimpling or other final molding used to impress adesired pattern to the-shell compresses the core material very slightlyat the points beneath the dimples or other surface indentations but theshell is sufficiently rigid to retain the dimpled or other impressedpattern sharply throughout the life of the ball despite any outwardpressure that may be exerted by the core and at the same time the shellis so thin and flexible that our ball presents all of the advantagespresented by the 'Barton ball.

The preferred rubbery material is a sulfur-vulcaniza- -ble copolymer ofbutadiene and acrylonitrile, typically containing from 15 to 45% byweight of'bo'und acrylonitrile, the balance being butadiene. Otherrubbery materials which are compatible with and plasticizers for thevinyl resin can be used. We almost invariably use a rubbery eopolymer ofan aliphatic conjugated diolefin hydrocarbon, especially butadiene, andanother copolymerizable monomer, especially acrylonitrile or a. homologthereof.

The core of our ball is preferably formed from a mixture of polyvinylchloride, butadiene-acrylonitrile rubbery copolymer and high-boilingorganic liquid plasticizer in relative proportions of from 30 to 125parts of the rubbery copolymer and from 60 to 80 parts of the liquidplasticizer per 100 parts of polyvinyl chloride. The total plasticizer,i. e., the sum of the rubbery copolymer and the organic liquidplasticizer, will generally range from 100 to 175 parts per 100 parts ofpolyvinylchloride.

Any suitable chemical blowing agent which will decompose upon heating attemperatures of 250 F. or thereabove to form a harmless gas, especiallynitrogen, and will form closed cells can be employed in making the core,examples being alpha, alpha'-azobisisobutyronitrile, diazoaminobenzene,p,p'-oxy bis (benzene sulfonyl hydrazide),dinitrosopentamethylenetetramine, etc. Selection of the blowing agentand the amount thereof are well within the skill of the art. The amountof blowing agent used is adjusted to yield the proper size of final ballat room temperature after the necessary expansion cycle. Corecompositions which yield balls which are too small require the use ofmore blowing agent while compositions which yield balls which are toolarge require less blowing agent. Generally the amount of active blowingagent will be from to 100 parts per 100 parts of polyvinyl chloride.

Curatives for the rubbery component are incorporated in the mixture usedin forming the core. These curatives comprise a vulcanizing agent,usually sulfur, an activator, usually zinc oxide in admixture withstearic acid, and, if desired, vulcanization accelerators of known type.Other conventional rubber compounding ingredients can be included.

In addition, it is desirable to include stabilizers of known type toprotect the rubber against deterioration. It may also be desirable toinclude a pigment such as titanium oxide. The compounding of the corematerial will be obvious from this disclosure.

The ingredients of the core stock are mixed together to a uniformmixture in any suitable manner after which the core stock is preferablyshaped into pro-forms having the correct volume and weight, the volumeof each preferably being substantially less than that of the miniaturemold cavity. By using a pre-form of lesser volume than the miniaturemold cavity we enable the miniature mold to be held completely closedunder moderate moldclosing pressure. All operations up to this point areconducted in the cold, using care not to heat the stock to such anextent as to decompose the blowing agent or pre-cure the rubbercomponent to an appreciable extent.

We prefer that the original stock be sufficiently deformable andputty-like in nature and sufficiently condensed (i. e., deusified toremove entrapped air) that pro-forms of exact weight and volume can bedinkedout from regularly or irregularly shaped pieces of the condensedcompound.

The preferred deformable and putty-like consistency of the originalcompound facilitates the loading of the small mold cavitie used in theminiature molding step by enabling the preparation of solid, easilyhandled, preforms of exact weight and volume for charging the individualminiature mold cavities, so that an expanded core of exactly the rightweight and volume is obtained. These solid pre-forms are not tacky orsticky and can be easily loaded into the miniature mold cavities. In thelight of this disclosure those skilled in the art can easily prepare astock of the desired putty-like consistency.

One way of making the preferred stock of putty-like consistency whichcan be accurately dinked-out into non-sticky pre-forms of exact weightand volume for use in the miniature molding step is to disperse amixture of powdered vinyl resin and the liquid plasticizer as thedisperse phase in a continuous phase of the rubber component. This canbe done by adding a, mixture of the resin and plasticizer to the bandedrubber on an open rubber mill, mixing being continued until a continuoussheet of well mixed compound is obtained. The other ingredients (blowingagent, vulcanizing agents, etc.) are incorporated in any suitable way;typically all of them but the rubber stabilizer are included in thedisperse phase by previously mixing them with the powdered resin andliquid plasticizer. Mixing temperatures are kept throughout as near roomtemperature as possible to prevent decomposition of the blowing agent.Incorporation of the ingredients in the foregoing way gives a non-stickydeformable stock of putty-like consistency which usually has appreciableresilience or nerve but which is ideally suited for the dinking-outoperation. The preforming (or dinking-out) of the stock is preferablydone by extruding or tubing to densify the compound and remove entrappedair, cutting off into pellets, and putting these pellets in sphericalmold cavities which have the exact volume desired for the pre-forms andwhich upon closing squeeze out the excess stock between the lands. It isoften desiralbe to pre-heat the pellets in an air oven at 200-300 F. forl0-20 minutes to render the stock softer and more yielding so that itdoes not spring back objectionably in this preforming step. Suchpre-heating is so conducted as not to decompose the blowing agent, fusethe mixture, or vulcanize the rubber.

When this deformable putty-like stock is used, the volume of thepre-forms should equal 78-96% of the volume of the miniature moldcavity. A figure of is preferred.

Instead of a deformable putty-like stock such as is described above, wecan less preferably employ a paste-like mixture of powdered rubber,powdered resin, liquid plasticizer and other components described herein. Thus we can take the commercially available materials known as GeonPolyblends which are colloidal" blends of polyvinyl chloride andbutadiencacrylonitrile rubber made by coagulation of mixed laticesthereof and blend them with suitable amounts of liquid plasticizer andwith blowing agent, curatives, etc., to give a paste-like mix which isthen passed several times through an extruder (e. g., a meat grinderequipped with a screen). We can then extrude a solid rod of the mixedstock and form it into pellets or biscuits which should be somewhatsmaller in volume than the miniature mold cavity, preferably of a volumeequal to -97% of the volume of the miniature cavity. This type of stockis objectionable because of its sticky nature and because it is notadapted to be accurately formed into pre-forms of exact weight andvolume.

Typically we then proceed as follows: We place the preforms in smooth,spherical mold cavities of a size much smaller than that of the finishedcore, typically /4 inch in diameter in the case where a practice golfball is to be made or 1.22 inches in case a practice baseball isdesired. We then subject these pre-forms to molding heat and pressure(using a temperature of at least 250 F. and a pressure sufiicient tohold the mold closed) to fuse the resin, rubber and plasticizer into asingle homogeneous phase, decompose the blowing agent to form gas whichis retained under pressure, either as small bubbles or in solution orboth, and at the same time partially vulcanize the rubber componentsutficiently to retain the gas as closed cells during the subsequentexpansion, vulcanization being completed in a later stage. In this stepwe use a temperature of at least 250 F. and more commonly at least 300F. We then cool the mold under pressure to approximately roomtemperature, remove the miniature cores from the mold and heat themunconfined at an elevated temperature, preferably at least 300 F., e.g., at 325-375 F. for 20-90 minutes, to complete vulcanization of therubber component and effect expansion to the greatest possible extentwhich is to a size much greater than that of the core of the finishedball. The expanded c'ores'iare next cooled toapprdximatelyj roomtemperature,

appearance. The expanded cores are now ready for the application of theshell.

It is essential that the core'be expanded in the unconfined expansionstep to a maximum size much greater than the sizeof the core in'thefinished'ball (typically to a. volume at least 25% greater than 'thecore of the final 'ball) and 'that'upon' cooling toroom temperature ithave the aforementioned wrinkled shrunken surface. Otherwise, thefinaIresult would not be a dimensionally stable ball. The highly unattractivewrinkled surface of the core issubsequently-concealed andat thesame'time' given durability by application of the shell.

The volume of the miniature mold is usually equal to from M; to that ofthe core of the finished ball.

Presence and vulcanization of the rubber component are essential fromthe standpoint of achieving-dimensional stability in the balls of ourinvention. The rubber permits expansion of the core composition attemperatures suflicientlyhigh 300 F. or'above) to relieve all internalstrains and stresses in a mannerwhich can be likened to the annealing ofmetals. Such relief of internal stresses and strains in this step is inlarge measure responsible f forthe're markable dimensional stability ofthe final core. Such'dimension'alstability is not possible if the rubberis "omitted or is not vulcanized.

We prefer to'form the shell of a'white pigmented solid mixture ofpolyvinyl chloride and a high-boiling organic liquidplasticizer'thereforin amount ranging from 30 to 80 parts of the plasticizer per 100 partsof polyvinyl chloride. As the high-boiling organic liquid plasticizer,we can use any plasticizer known to be capable of plasticizing polyvinylchloride. Generally these liquid plasticizers are ethers or esters.Examples are dioctyl -phthalate, dibutyl sebacate, dioctyl sebacate,tricresyl phosphate, dibutyl phthalate, linear polyesters, etc. Weprefer to employ in the shell compound suitable proportions ofstabilizers for the polyvinyl chloride, and suitable proportions ofwhite pigment, especially titanium dioxide.

We prefer to form the shell by dipping the expanded cores in a whitepigmented organic solvent'solution of the shell compound, typicallyapplying two or three coats. of

this paint as required to give the proper shell thickness, the thicknessof each coat typically ranging from 0.5 to 4 mils, with proper dryingtimes between coats and after the final coat. We then give the dried,painted balls a light dusting with a mold parting agent such as zincstearate and then subject them to a refrigeratingo'r freezing operation'to cool them to a low temperature, preferably below 40 F., to contractthem 'to a size substantially less than the 'fin'al size 'o'fth'e balls,in preparation for final molding 'to impress the desired surface patternon the shell and give a perfectly spherical ball. We then place Z-thecold balls in a cold finalsurface-forming mold typically having thedesired final diameter, e. g., 1.72" inthe case of a golf ball or 2.93"in case of a baseball. The balls should be so contracted by the coolingstep as not to extend over 'the'lands of the mold which would have theundesirable result of cutting oif of a portion of the balls by theclosing mold halves and giving a defective ball. The molds are thenclosed and subjected to suitable heat and pressure to eflectsurfaceshaping of the shell. In the case of a golf ball we usually use 600-1200lbs. per cavity :pressure and heat 415 minutes at 300 F. We'then coolthe surface shaping molds down to room temperature while keeping themolds under pressure and remove the balls which are now finished exceptfor application of colored paint to fill branding or stitchingindentations, this being an incidental operation.

In the drawings, a Ipre-form 1 (Fig. 1) of raw puttylike core stock(which was pre-formed by the above-de- F scribed dinking-out operationwhich caused the forma "non ofig'r'oove Ia around tlre extmded'p'elletofstpck) is placed between miniature mold halves 2 and 3, which togetherform a-smoothmold cavity in'diameter, and the mold halves 'are closedtogether. The pre-form 1 is then molded under 'heat and pressure in theminiature 'mold, yielding a miniature spherical core 4 (Fig. 3)

which contains minute bubbles of gas under pressure and/or gas insolution. After thoroughly cooling the mold, the mold halves 2 and 3 areseparated and core 4 is removed,'exp'andin'g slightly as it-is releasedfrom the mold cavity, expansionbeing greater from a mold which is lesscooled. The core4' is then heated upon open'tray '5 in circulating airto a suitably elevated temperature (preferably 32'5-3 7 5" F.) andexpanded to form thecore fi'which has a roughly spherical "shape and atthis point is much larger than the core of the finished'ball. After theexpansion step the core 6 iscooled to room tempera- 'agentand subjectedto freezing "(i. e. refrigeration) to shrink it so that it will fit intoa 1.72" dimpled mold cavity formed by dimpling moldhalves 8. and 9 ofFig. 6 without extending over the lands of the mold which would causethe core to be cut by the closing mold halves 8 and 9 and result inadefective ball. The mold halves 8 and 9 are then closed under pressureand the mold is then 'heated under pressure to effect-the dimpling afterwhich it is cooled to atemperature'approaching room temperature.

This operation yields the finished practice golf ball 10 having thedimples 11 over itsentire outer surface, these dimples being formed bydeformation of the shell 7 and core 6 so as to closely simulate anordinary .golf ball. If desired, a name brand can be engraved on theinterior of the dimpling mold formed by halves Sand 9 so that the namebrand is transferred to the shell 7 during the dimpling operation Thebranding indentations are subsequently filled with a colored paint tomake the brand name legible.

Instead of using a vinyl resin as the basis of the shell composition, wecan use "other thermoplastic resins which aretough and flexible, orbecomeso upon plasticization, which are soluble in organicsolvents so asto permit application to the core, which give a tack-free,water-resistaut, abrasion-resistant and wear-resistant surface, whichallow the core of the finished ball to be deformed indefinitely in play,e. :g., under the blows of the golf club,

which allow the ball to assumeitsoriginal shape immediately afterremoval'of the deforming force, which are capable of'tightly adhering tothe core, and which are capable of being given sharp definition in thefinal shellm'oldi'ng operation and of retaining this sharp definitionindefinitely. Examples of other thermoplastic resins are polymethylacr'ylate, polyethyl 'ac'rylate, polymethyl methacrylat'e,polyethyl'methacrylate, etc., and copolymers of various alkylacrylatesand 'alkyl methacrylates. If the resin is not sufficiently flexible, 'aplasticizer should be vr sion of the core. The coating should dry at atemperature of not 0ver'140 F. Mild heat (-not over F.) to acceleratedrying of room temperature coatings is permissible. There should be atleast 30 minutes of drying at room temperature between coats to insureadequate drying.

Although the relative proportions of core and shell in the finished ballcan vary widely without departing from the spirit of our invention,typically the shell makes up from to 40% by weight of the finished balland from 1 to 4% by volume thereof, the core correspondingly making upfrom 80 to 60% by weight and from 99 to 96% by volume of the ball.

A practice golf ball made by our invention has substan tially the samediameter as a regulation golf ball which at present is 1.68 in diameter.However, the diameter can vary somewhat from this figure, for examplefrom 1.65 to 1.80". A practice baseball will usually have a diameter ofapproximately 2.9 inches, where a hard baseball is simulated. If asoftball is simulated it will of course be larger.

The core of our ball is characterized by its extremely light weight, itsdensity generally not exceeding 8 lbs. per

cubic foot and more commonly not exceeding 5 lbs. per

cubic foot.

The total weight of our practice golf ball will generally be from 60 to100 grains. Our practice baseball will usually weigh from 300 to 350grains.

The following examples illustrate our invention more fully.

EXAMPLE 1 Core compound Ingredients: Parts by weight Polyvinyl chloride100 Butadiene-acrylonitrile rubbery copolymer containing about combinedacrylonitrile 100 Ester-type liquid plasticizer 65 Unicel NDdinitrosopentamethylene- All of the foregoing ingredients except therubbery copolymer and rubber antioxidant were mixed together in a powdermixing blender. The rubbery copolymer and rubber antioxidant were milledon a conventional two roll rubber mill until banded. The blend ofpowders and liquid prepared in the powder mixing blender was then addedto the banded rubber, mixing being continued until a continuous sheet ofwell-mixed compound was obtained. Mixing temperatures were maintainedthroughout as near to room temperature as possible to prevent prematuredecomposition of the blowing agent. The resulting sheet was thenextruded while cold into a rod of stock, this operation serving todensify the compound by removing entrapped air so that shaped pre-formsof stock having precise volume and weight could be prepared by aconventional procedure. These pre-forms were then made by a dinking-outstep in which a length of extruded stock representing an excess wasplaced between two hemispherical mold cavities so that the cavity wasentirely filled with compound and the excess stock was squeezed beyondthe mold cavity lands by the closing pressure of the mold halves. Thisdinking-out was done in the cold and yielded pre-forrns which due to theresilience of the stock sprang into the irregular shape shown in Fig. 1upon opening the preforming mold, groove 1a being formed along the lineof removal of the flash in the dinking-out operation. These preforms hada volume equal to approximately 88% of the miniature mold cavity volume.These pre-forms were then molded in miniature in a 4 diameter smoothsurfaced miniature mold under a closing pressure of 4,000 lbs. percavity and at a temperature of 335 F. for 20 minutes whereupon the moldswere cooled while 8 under pressure to bring the miniature molded ballsto below 120 F. The molds were then opened and the smooth-surfacedpartially cured miniature balls were then removed. There was some slightexpansion of the balls as they were released from the mold cavity. Thepartly cured balls were then heated on an open tray in circulating airat 365 F. for about 60 minutes. During this expansion and heat treatmentcertain volatiles were removed from the balls inasmuch as they lostabout 15% of their original weight during this treatment. Vulcanizationof the rubber component was now complete. The expanded balls were notperfect spheres but were slightly irregular. This irregularity wascompletely removed in the subsequent dimpling operation applied to theshell.

The expanded balls were then cooled to room temperature and dipped intoa solvent solution of paint having the following formulation.

Shell compound or paint Ingredients: Parts by weight Polyvinyl chloride100 Ester-type liquid plasticizer 53 Stabilizers for polyvinyl chloride6 Titanium oxide 20 Methyl ethyl ketone (solvent) 537 Three coats of theforegoing paint were applied with drying between coats. The driedpainted balls were then contracted by cooling to a diameter such thatthey would not be cut by the dimpling mold and then dimpled in exactlythe manner described above using dimpling molds having a diameter of1.720". The finished balls had the following composition:

By By Component Weight, Volume,

grains percent Closed-cell Core (compound given above) 52 97 Non-porousShell formed of 3 coats of above vinyl paint 28 3 EXAMPLE 2 Example 1 isduplicated exactly except that the stock used for making the core hasthe following formulation and expansion is accomplished with less heat.

Core compound Ingredients: Parts by weight Geon Polyblend 50OX479;(polyvinyl chloride, butadiene-acrylonitrile copoly- This formulationwas prepared by blending all of the powders together, separately mixingboth liquids together and adding the mixed liquids to the powders withstirring until all three liquids had been absorbed. The mixture was thentumbled for 15 minutes to give complete mixing. The resulting blend waspassed through a meat grinder equipped with a 20 mesh screen for ninepasses. The tubing attachment was then placed on the meat grinder and onthe tenth pass a solid rod of mixed compound Was extruded. This rod wascut off into pellets which were formed into preforms which wereprocessed into final balls in the same manner as in Example 1, exceptthat the partly cured balls were heated on an open tray in circulatingair for about 20 minutes at 325 F.

in some cases, when using a paste-like core compound like that used inExample 2, it is helpful in getting a 9 good dispersion of stabilizers,etc., to withhold about of the plasticizer until the mixture has beengiven several passes through the moat grinder whereupon the withheldplasticizer is, added and the mixture is .given the remaining passesthrough the grinder.

EXAMPLE 3 EXAMPLE 4 Example 1 was duplicated essentially except that apractice baseball was made. The .pre-form waslarger, having a weight of290 grainsand the pro-form die had a cavity diameter of 1.22". The stockbiscuits had a volume of approximately 88% of the miniature mold cavitywhich was formed by two smooth surface hemispherical mold halves havinga diameter of 1.27. The

miniature mold was closed under a pressure of 9,750

pounds per cavity minimum clamping force and the miniature was cured forminutes to 335 F. in this mold.

The miniature cured core was expanded for 60 minutes at 365 F. Againabout 15% loss of weight occurred during the expansion. Three coats ofthe vinyl paint were applied, giving a shell weight of 90 grains. Aftercooling by freezing the ball was molded in an engraved finishing moldhaving a diameter of 2.93" to simulate the surface of a baseball. Themold was closed and the ball was molded for 15 minutes at 300 F. andcooled under pressure for 15 minutes to room temperature. This formedsimulated seams, stitching and branding. The seam, stitching andbranding indentations were then filled with a colored .paint. The finalball had a diameter of 2.9:.1 inch, and had the following composition:

By By Component Weight, 7 Volume, Grains Percent Gore .i 2 46 98 Shell90 2 The resulting ball (which is portrayed in Fig. 7) was very suitableas a play ball which would not injure people or objects struck by it.

Although we have described our invention with specific reference topractice golf balls and baseballs, our invention can be used to make anytype of practice or play ball exhibiting lightness, close simulation inappearance of conventional balls, and complete freedom from danger topersonnel or property. A. beach ball is an example. The halls of ourinvention are completely water-impervious and will float indefinitely onwater and do not readily pick up dirt. Should they become dirty they caneasily be cleaned.

As the resinous component in our core and shellwe generally usepolyvinyl chloride or a copolymer of a major proportion, say 85-99%, ofvinyl chloride and a minor proportion, say 151%, of vinyl acetate.Instead of using a vinyl chloride-vinyl acetate copolymer, we can useany other similar thermoplastic copolymer of a major proportion of vinylchloride and a minor proportion of another copolymerizable monomer suchas methyl acrylate, diethyl maleate, vinylidine chloride, etc. Thesevinyl resins all possess the necessary property of being fullycompatible with the rubbery copolymer used in the core. The copolymersreferred to are considered to be equivalent to polyvinyl chloride.

From the foregoing description it will be seen that our inventionprovides a practice ball having all of the of a regular ball.

appearance of a regular ball.

' 10 iadvantages-of'the ball shown by Barton. Thus,=ourball, not onlyinitially but throughout its long life, has the dimensions, shape andappearance of a regulation -ball and is characterized by its lightweight, deadness, short flight, freedom from hazard in use, and abilitytosubstantially duplicate on a small scale the flight behavior Inaddition it has far greater dimensional stability and simulates muchmore closely the The introduction of the vulcanized rubber component intheclosed-cell structure is responsible for markedly improveddimensionalstabil- 'ity but it materially decreases the durability ofthe closed- -cell structure so that it will not withstand'normal playingusage, e. g., successive hard golf club drives. Also, the

maximum expansion followed by shrinkage gives an {unattractive wrinkledsurface which would not be saleable.

However, the novel shell completely overcomes these defects,contributing the required durability and wearresistance, and addsgreatly to the appearanceandflclose simulation of a regulation ball, byvirtue of its ability to take and retain sharp surface definition for-anindefinite period of time. The shell protects'the core against failureby reason of its tough flexible nature and the tenaciousness with whichit is adhered to the core.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:

1. As a new article of manufacture, a practice or play ball comprisingan inner spherical core formed of a flexible compressible resilientclosed-cell expanded uniform mixture of a thermoplastic resin selectedfrom the .group consisting of polyvinyl chloride and copolymersof amajor proportion of vinyl chloride and a minor proportion of anothercopolymerizable monomer, a vulcanized rubbery copolymer of an aliphaticconjugated diolefin hydrocarbon and another copolymerizable monomer,said rubbery copolymer before vulcanization being compatible with saidresin, and high-boiling organic liquid plasticizer for said resin, saidcore having a density of not over 8 pounds per cubic foot, and a thincontinuous unexpanded plastic shell surrounding said core, said shellcomprising a layer of ,plasticized thermoplastic resin selected from thegroup consisting of polyvinyl chloride and copolymers of a majorproportion of vinylchloride and a minor prointegrally bonded to saidcore, said shell constituting from 20 to' 40% by weight and from 1 to 4%by volume of the ball, being capable of taking and maintaining sharpsurface pattern definition over a long period of time, being tough andhighly wear-resistant, protecting said core against failure in service,being flexible and tenaciously adherent to said core, being so flexiblethat the ball has substantially the playing behavior of the core alone,and permitting deformation of said core indefinitely in play withoutseparation or cracking of said shell.

2. As a new article of manufacture, a practice or play ball comprisingan inner spherical core formed of a flexible compressible resilientclosed-cell expanded uniform mixture of a thermoplastic resin selectedfrom the group consisting of polyvinyl chloride and copolymers of amajor proportion of vinyl chloride and a minor proportion of anothercopolymerizable monomer, a vulcanized butadiene-acrylonitrile rubberycopolymer which before vulcanization is compatible with said vinylresin, and high-boiling organic liquid plasticizer for said vinyl resin,said core having a density of not over 8 pounds per cubic foot, and athin continuous unexpanded plastic shell surrounding said core, saidshell comprising a layer of a mixture of a thermoplastic resin selectedfrom the group consisting of polyvinyl chloride and copolymers of amajor proportion of vinyl chloride and a minor proportion of anothercopolymerizable monomer and highboiling organic liquid plasticizer forsaid vinyl resindeposited directly on said core by drying from asolution of said resin and a high-boiling organic liquid plasticizertherefor in a volatile organic solvent, said layer being directly andintegrally bonded to said core, said shell constituting from to 40% byweight and from 1 to 4% by volume of the ball, being capable of takingand maintaining sharp surface pattern definition over a long period oftime, being tough and highly wear-resistant, protecting said coreagainst failure in service, being flexible and tenaciously adherent tosaid core, being so flexible that the ball has substantially the playingbehavior of the core alone, and permitting deformation of said coreindefinitely in play without separation or cracking of said shell.

3. As a new article of manufacture, a practice or play ball comprisingan inner spherical core formed of a flexible compressible resilientclosed-cell expanded uniform mixture of a thermoplastic resin selectedfrom the group consisting of polyvinyl chloride and copolymers of amajor proportion of vinyl chloride and a minor proportion of anothercopolymcrizable monomer, a vulcanized butadiene-acrylonitrile rubberycopolymer which before vulcanization is compatible with said vinylresin, and highboiling organic liquid plasticizer for said vinyl resin,the foregoing components being employed in relative proportions of fromto 125 parts of said rubbery copolymer and from 60 to 80 parts of saidplasticizer per 100 parts of said vinyl resin, said core having adensity of not over 8 pounds per cubic foot, and a thin continuousunexpanded plastic shell surrounding said core, said shell comprising alayer of a mixture of a thermoplastic resin selected from the groupconsisting of polyvinyl chloride and copolymers of a major proportion ofvinyl chloride and a minor proportion of another copolymerizable monomerand high-boiling organic liquid plasticizer therefor in relativeproportions of from 30 to 80 parts of said plasticizer per 100 parts ofsaid vinyl resin deposited by drying from a solution of said resin andsaid plasticizer in a volatile organic solvent, said layer beingdirectly and integrally bonded to said core, said shell constitutingfrom 20 to by weight and from 1 to 4% by volume of the ball, beingcapable of taking and maintaining sharp surface pattern definition overa long period of time, being tough and highly wear-resistant, protectingsaid core against failure in service, being flexible and tenaciouslyadherent to said core, being so flexible that the ball has substantiallythe playing behavior of the core alone, and permitting deformation ofsaid core indefinitely in play Without separation or cracking of saidshell.

4. The method of making a practice or play ball which comprises moldinga miniature spherical core containing gas under pressure from a mixtureof a thermoplastic resin selected from the group consisting of polyvinylchloride and copolymers of a major proportion of vinyl chloride and aminor proportion of another copolymerizable monomer, a vulcanizablerubbery copolymer of an aliphatic conjugated diolefin hydrocarbon andanother copolymerizable monomer, said rubbery copolymer beforevulcanization being compatible with said vinyl resin, a high-boilingorganic liquid plasticizer for said vinyl resin, a chemical blowingagent, and a vulcanizing agent for said rubbery copolymer, under suchconditions as to decompose said blowing agent, partially vulcanize saidrubbery copolymer so that it will retain the gas evolved by the blowingagent, and yield a miniature core in which said vinyl resin, rubberycopolymer and plasticizer constitute a single homogeneous phase and inwhich the generated gas is retained under pressure, expanding saidminiature core to closed-cell form. in which it has a volume at least25% greater than the core of the finished ball and completingvulcanization of said rubbery copolymer by applying heat to the corewhile it is free to expand, cooling the expanded core to approximatelyroom temperature to shrink it to a size approximating the core of thefinished ball and impart a wrinkled shrunken surface thereto, applyingdirectly to the resulting core a thin continuous shell of a toughflexible unexpanded and unexpandable plastic material capable ofreceiving and maintaining sharp surface pattern definition, said shellconstituting from 20 to 40% by weight and from 1 to 4% by volume of thefinished ball and comprising a layer of a mixture of a thermoplasticresin selected from the group consisting of a polyvinyl chloride andcopolymers of a major proportion of vinyl chloride and a minorproportion of another copolymerizablc monomer and a hi gh-boilingorganic liquid plasticizer and being deposited directly upon said coreby drying from a solution of said resin and said plasticizer in avolatile organic solvent, said shell being so flexible that the finishedball has substantially the playing behavior of the core alone andallowing the core of the finished ball to be deformed indefinitely inplay without separation of said shell from said core, contracting thecoated core to a size substantially smaller than the final ball bycooling below room temperature, and imparting a surface pattern to thecoating of the contracted coated core by molding the same under heat andpressure to form the finished ball the core of which has a density notexceeding 8 pounds per cubic foot.

5. The method of claim 4 wherein said core-forming mixture containspolyvinyl chloride, a butadieneacrylonitrile rubbery copolymer, andhigh-boiling organic liquid plasticizer in relative proportions of from30 to 125 parts of said copolymer and from 60 to parts of saidplasticizer per parts of said polyvinyl chloride, and wherein said shellis formed from a mixture of polyvinyl chloride and a high-boilingorganic liquid plasticizer therefor in relative proportions of from 30to 80 parts of said plasticizer per 100 parts of said polyvinylchloride.

6. The method of making a practice or play ball which comprises forminga pre-form of a deformable mixture of putty-like consistency comprisinga thermoplastic resin selected from the group consisting of polyvinylchloride and copolymers of a major proportion of vinyl chloride and aminor proportion of another copolymerizable monomer, abutadiene-acrylonitrile rubbery copolymer which before vulcanization iscompatible with said vinyl resin, high-boiling organic liquidplasticized for said vinyl resin, a chemical blowing agent, and avulcanizing agent for said rubbery copolymer, said rubbery copolymerbeing in the continuous phase and said vinyl resin and liquidplasticizer being in the disperse phase, said pre-form having a volumeof from 78 to 96% of that of the hereinaftermentioned spherical moldactivity, molding this pre-form under heat and pressure in asmooth-surfaced spherical mold cavity having a volume of from A, to thatof the core of the finished ball and thereby decomposing said blowingagent, partially vulcanizing the rubbery material so that it will retainthe gas evolved by the blowing agent, and thereby forming a miniaturespherical core in which said vinyl resin, rubbery copolymer andplasticizer constitute a single homogeneous phase and in which thegenerated gas is retained under pressure, heating said core while it isfree to expand to complete vulcanization of said rubbery copolymer andcause maximum expansion to closedcell form having a volume at least 25%greater than the core of the finished ball, cooling the expanded core toapproximately room temperature to shrink it to a size approximating thecore of the finished ball and impart a wrinkled shrunken surfacethereto, applying to the resulting core a thin continuous unexpandableplastic shell comprising a layer of a thermoplastic resin selected fromthe group consisting of polyvinyl chloride and copolymers of a majorproportion of vinyl chloride and a minor proportion of anothercopolymerizable monomer, said last-named vinyl resin being plasticizedwith high-boiling organic liquid plasticizer, said layer being depositedon said core by drying from a solution of said resin and saidplasticizer in a volatile organic solvent, said shell constituting from20 to 40% by weight and from 1 to 4% by volume of the finished ball,being capable of receiving and maintaining sharp surface definition,being so flexible that the finished ball has substantially the playingbehavior of the core alone and allowing the core of the finished. ballto be deformed indefinitely in play without separation of said shellfrom said core, cooling the coated core below room temperature tocontract it to a size substantially smaller than the final ball, andimparting a surface pattern to the coating of the contracted coated coreby molding under heat and pressure to form the finished ball the core ofwhich has a density not exceeding 8 pounds per cubic foot.

14 UNITED STATES PATENTS Voit Apr. 25, Eden Dec. 27, Daly et a1. Nov. 2,Barton Oct. 11, Smith Oct. 17, Daly et a1. Oct. 9,

FOREIGN PATENTS Great Britain Nov. 29,

